As technology nodes decrease, stacking circuits on top of one another is used to reduce an overall size of an integrated circuits. Stacking circuits includes forming electrical connections between the stacked circuits in order to transfer signals between different portions of the integrated circuit. Contact pads are commonly used to electrically connect the stacked circuits. If contact pads between different portions of the stacked circuits are not properly aligned, a risk of an open circuit or a short circuit is increased.
In some approaches, alignment marks are used to help align contact pads of the stacked circuits. The alignment marks are formed in a portion of the circuit away from functional components. An alignment mark of an upper circuit is positioned above an alignment mark of a lower circuit. The goal is that matching the alignment marks atop one another will result in an alignment between contacts pads on the upper circuit and contact pads on the lower circuit.
In order to achieve the goal of aligning the contact pads based on the alignment marks, a complete graphic database system (GDS) file for all stacked circuits is used. The complete GDS file includes the layout of each stacked circuit. Any adjustments within any one of the stacked circuits which changes a location of a contact pad is propagated through all stacked circuits to maintain proper alignment of contact pads in a completed circuit. In order to determine whether the designed stacked circuits are properly aligned, a test circuit is manufactured and tested in order to determine whether any open circuits or short circuits are present in the design.